1. Field of Invention
The present invention relates to an electronic timepiece that uses power produced by photovoltaic generation as a power source and has a function for receiving microwaves.
2. Description of Related Art
Electronic timepieces that receive microwave signals and acquire information superposed on a microwave carrier signal are being developed. For example, wristwatches have been developed that acquire the current position, date, and accurate time information by using the Global Positioning System (GPS), which is a system in which satellites (GPS satellites) orbiting the Earth on known orbits transmit microwave signals (satellite signals) carrying superposed time information and orbit information, and terrestrial receivers (GPS receivers) receive these microwave signals (satellite signals) to determine their own positions. Such wristwatches are taught in Japanese Unexamined Patent Appl. Pub. JP-A-2000-138607 and in Japan Patent No. 4044898.
A problem with the wristwatches taught in JP-A-2000-138607 and in Japan Patent No. 4044898, however, is that because the antenna is housed is a protrusion that can be seen from the outside, timepiece appearance and wearability are impaired and even the ease of use is a problem. A conceivable solution for such wristwatches is to make the dial from a material that passes microwaves and dispose the antenna on the back side of the dial in order to improve both the appearance and wearability.
Wristwatch-type radio-controlled timepieces that use electricity produced by photovoltaic generation by solar cells and receive 40-kHz or 60-kHz standard time signals are also known from the literature. Solar cells are generally designed so that the area to which light is incident is as large as possible in order to increase photovoltaic efficiency. As a result, in consideration of the appearance and wearability, the solar cell may be disposed so that the surface of the solar cell is opposite substantially the entire area of the back side of the dial in a wristwatch-type radio-controlled timepiece with a solar cell. This means that the standard time signal will be received through the solar cell if the antenna is disposed on the back side of the dial, but because the standard time signal is a long wave, low frequency signal, the solar cell has substantially no effect as a standard time signal shield and there is no effect on standard time signal reception performance.
However, because the shield effect of the solar cell to high frequency microwave signals is extremely strong and reception performance is thus degraded, there has been no attempt to render an electronic timepiece that receives microwaves with a solar cell while also disposing the antenna on the back side of the dial in order to improve appearance and wearability.